Locked into an extreme tomorrow: Multi-hazard analysis reveals unprecedented regional rates of change of extreme weather events until 2040, even for drastically reduced emissions

Climate change is causing a range of weather phenomena to move outside the range to which people and ecosystems are adapted. Much attention has been given to absolute changes, such as average temperatures or changes to the return values of extreme events, with global warming. However, the rate of change, and how that compares to the rates of change experienced in the preindustrial climate, i.e. the amount of change we have previously experienced over a short time period, is also an important determinant of impacts, and yet has not been given as much attention. In particular, as climate extremes are responsible for a disproportionate share of impacts, society can be expected to be particularly vulnerable to high rates of change of extremes – especially when multiple hazards increase at once.

Using large ensembles of climate model simulations, we examine rates of change of temperature and precipitation extremes, both separately and combined, over the next twenty years (2021-2040) and compare with 20-year rates of change in the pre-industrial (PI) period. We consider regional scales, due to their increased relevance to the experience of people and ecosystems compared to global mean changes. We find that for many sub-continental-scale regions, the rates of change over the next twenty years will shift substantially away from the distribution of trends simulated in the preindustrial period. In more than a third of the regions studied, ensemble mean combined rates for both extremes types are at least two standard deviations greater than PI variability of trends, and more than one standard deviation greater in almost all regions under a high emissions scenario (SSP5-8.5). Substantial changes are also seen in a scenario with drastically reduced emissions (SSP1-2.6). Low latitude regions are particularly affected due to their small internal variability in temperature extremes trends. These tend to be low-income countries that are particularly vulnerable to the impacts of climate change. Changes in rates are most obvious for temperature extremes, but a number of regions also experience substantial simultaneous changes in rates for precipitation extremes.  In low emission scenarios, the rates of change tend to flatten out in subsequent 20-year periods, but accelerate in the highest emissions scenarios.

Notably, we find that rapid reductions of anthropogenic aerosols over the next twenty years in low emissions scenarios lead to accelerated increases of both hot and wet extremes over India and parts of China, due to the compound effects of surface warming from greenhouse gas warming and loss of cooling from atmospheric aerosols

These findings have important implications for climate policy, decision making and near-term adaptation strategies. However, despite the emerging signal of rapid 20-year rates of change, spread amongst ensemble members is nevertheless large, particularly in the mid to high latitudes, meaning that trends of the opposite sign are not impossible in the near term, even if not that probable. This is also an important consideration to take into account when communicating these, and other, results on near-term decadal rates of change.